Thermostatic mixing valve

ABSTRACT

A thermostatic mixing valve having a hot water inlet for connection to a supply of hot water, a cold water inlet for connection to a supply of cold water, an outlet for temperature controlled water and a valve device for controlling the relative proportions of hot and cold water admitted to a mixing chamber. The outlet communicates with the mixing chamber to receive temperature controlled water having a desired temperature. A temperature control adjusts the valve device in accordance with the desired temperature of the temperature controlled water where the valve device and the mixing chamber form flow passages for the incoming streams of hot and cold water and are configured such that the velocity of the incoming water streams is maintained and the incoming water streams are turned to flow in the same direction so that flow of one stream can entrain and assist flow of the other stream.

PRIORITY CLAIM

This application is a continuation application of and claims the benefitof U.S. patent application Ser. No. 11/804,631 filed on May 18, 2007,which is a continuation application of and claims the benefit of U.S.patent application Ser. No. 10/607,025, filed on Jun. 26, 2003, now U.S.Pat. No. 7,240,850, each application being incorporated herein in theirentireties.

FIELD OF THE INVENTION

This invention concerns improvements in or relating to thermostaticmixing valves. The invention has particular, but not exclusive,application to thermostatic mixing valves for water supply installationssuch as showers.

BACKGROUND

Thermostatic mixing valves provide a source of water having a desiredtemperature and are operable to maintain the desired water temperaturesubstantially constant. Typically, the desired water temperature isobtained by controlling the relative proportions or hot and cold wateradmitted to a mixing chamber and adjusting the relative proportions tomaintain the desired water temperature substantially constant.

The known thermostatic mixing valves employ an actuator responsive towater temperature for adjusting the relative proportions in which thehot and cold water are mixed to maintain the desired water temperaturesubstantially constant. Various types of actuators for providing thethermal control of the water temperature are known including thermallyresponsive elements positioned in the water flow for actuating the valvein response to the detected water temperature. For example, wax capsulesor bimetal or memory metal type actuators. Alternatively, a motor may beprovided to actuate the valve in response to the water temperaturedetected by temperature sensors.

In use, the outlet water temperature can deviate from the desiredtemperature if the temperature and/or pressure of one or both of the hotand cold water supplies to the mixing valve changes. A sudden increaseor decrease in temperature that is sufficient to be discernible to theuser may result in an uncomfortable experience. As a result, steadystate temperature performance requirements are becoming increasinglymore stringent with reductions in the permitted temperature deviationsbeing introduced. For example, in mixing valves for healthcareapplications such as in hospitals or care homes for the elderly ordisabled, temperature deviations of only a few degrees are permitted.

In addition to steady state temperature performance requirements,transient temperature performance requirements dealing with temperatureovershoots or undershoots when the operating conditions suddenly changeare increasingly being included in valve specifications for certainapplications, especially in the healthcare market. Transient temperaturechanges typically arise when the desired water temperature is changed,for example from cold to hot or where the valve is initially turned on.Under these conditions, the valve may initially change the relativeproportions of hot and cold water more than is required before settlingto produce water having the new desired temperature. The size andduration of any temperature overshoot or undershoot may only last a fewseconds but is again discernible to the user if more than a few degreesand can be uncomfortable even if not presenting a safety risk.

A common approach to meet these tighter performance standards has beento seek to improve the thermal control system and in particular theaccuracy and speed of response of the system to detected changes in thedesired temperature of the water. This approach is based on theassumption that the water has been properly mixed so that the systemresponds equally to any changes tending to increase or decrease thedesired water temperature.

This approach has not been completely successful, however, and in manycases valve performance is generally not as good as predicted bytheoretical calculations. Often the valve responds more to changes inone water supply than the other and the thermal control system isadapted by trial and error to produce an arrangement in which theresponse is consistent to changes in either supply. In particular, theoutlet water temperature may deviate from that selected if the inletpressures change and skewing the response of the valve to inlet pressurechanges may be required to ensure that any deviation of the outlet watertemperature fits within a permitted tolerance range. Such skewing of theresponse is undesirable however as it may not result in optimumperformance for all the circumstances that may arise in use.

As a result of extensive testing, we have now found that in manyexisting valve designs incomplete mixing of the water occurs and thewater temperature detected by the thermal control system is made up ofthe temperature of partially mixed and unmixed streams of hot and coldwater. Indeed, for some designs, as little as 25% of the water stream ismade up of mixed water having the desired temperature.

Typically, the waterways within the valve are made up of spaces betweenvalve components and are not particularly streamlined. This can producevariations in the flow through the valve which, together with incompletemixing of the water, is now believed to be a reason for quitesignificant variations in performance occurring from one valve toanother. For example, we have found that when a valve that fails to meetthe required performance standards during testing is taken apart, thereis often nothing wrong with it and, when re-assembled with the samecomponents, the valve can pass the performance standards on re-testing.

As a result, a considerable amount of time and attention has been spentin ensuring that only valve components of the highest quality are usedand that assembly is carried out very carefully. This adds considerablyto production costs and the fundamental problem of variations inperformance between valves assembled from the same components stillpersists.

The present invention has been made from a consideration of theaforementioned disadvantages and drawbacks of existing thermostaticmixing valves.

SUMMARY

It is a desired object of the present invention to provide an improvedthermostatic mixing valve that is operable in a reliable manner.

It is yet another preferred object of the present invention to providean improved thermostatic mixing valve having performance characteristicsconsistent with theoretical calculations.

It is a still further desired object of the present invention to providean improved thermostatic mixing valve having application toinstallations for different requirements.

Other preferred objects of the present invention will be apparent fromthe description later herein of exemplary embodiments.

According to a first aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water, eachinlet communicating with a multi-stage plenum chamber constructed andarranged to distribute flow of water to porting of the valve means foradmitting the water to the mixing chamber.

By this invention, the incoming flows of hot and cold water are managedto produce conditions that reduce asymmetric flow patterns and promotethorough mixing of the water flows. As a result, a faster, more accurateresponse to change in the outlet water temperature can be achieved bothfor steady state operation to maintain a desired outlet watertemperature substantially constant and to reduce transient temperatureovershoots/undershoots when the desired outlet water temperature isadjusted by the user.

This approach to manage the incoming water flows is totally different tothe prior art. More especially, the present invention recognises andprovides a solution to the problems of incomplete mixing of the hot andcold flows on the accuracy and reliability of the thermal controlsystems employed to adjust the relative proportions of the hot and coldflows. In particular, the present invention enhances the mixing of thehot and cold flows by distributing the flows uniformly with respect tothe porting for admitting the flows to the mixing chamber.

In this way, the development of asymmetric flow patterns that tend tokeep the flows separate is reduced or eliminated. As a result,substantially complete mixing of the flows to provide a fully blendedflow can be achieved within a mixing chamber of relatively small volume.This enables detection of the outlet water temperature to be carried outsoon after the flows have been brought together and enhances theresponse of the valve to changes in the desired water temperature.

Each inlet preferably communicates with an annular outer chamber of atwo stage plenum chamber having an annular inner chamber separated fromthe outer chamber by partition means arranged so that water flows aroundthe outer chamber and into the inner chamber at a position axiallyspaced from the porting of the valve means.

In this way, the water is initially distributed around the outer chamberand approaches the porting in an axial direction within the innerchamber. As a result, swirling flow vectors are significantly reduced asthe water approaches the porting and the distribution of water volumeand velocity energy is substantially even around the porting for bothflows. This produces essentially identical mixing conditions for bothflows entering the mixing chamber that in turn leads to enhanced mixingthat avoids the formation of separate streams of mixed and unmixedwater.

Preferably, each plenum chamber is of similar size and shape so that thedistribution of flows is substantially the same. As a result, both flowsare matched so that any asymmetry is cancelled out when the flows mergewithin the mixing chamber. In this way, conditions in which separatestreams of mixed and unmixed water may be formed are eliminated to alarge extent.

The partition means separating the outer and inner chambers may be anannular wall provided with at least one opening for water to flow intothe inner chamber. Preferably, the opening provides a substantiallyuniform distribution of the water flow around the inner chamber. Forexample, the opening may be in the form of a continuous annular slot inthe wall between the outer and inner chambers. Alternatively, theopening may be in the form of a series of slots or holes of uniform sizeand shape formed in the wall between the outer and inner chambers with aregular spacing between the slots in the circumferential direction.

Preferably, the opening is offset relative to the point at which thewater flow enters the outer chamber. In this way, the water is preventedfrom flowing directly into the inner chamber and is confined to flowaround the outer chamber. This further contributes to a uniformdistribution of water flowing towards the porting within the innerchamber.

In a preferred arrangement, the opening is axially offset relative tothe point at which the water flow enters the outer chamber. In this way,the water flow is distributed around the outer chamber and approachesthe opening in an axial direction before flowing into the inner chamber.This leads to a further reduction in swirling flow vectors and enhancesuniform distribution of the water flow towards the porting within theinner chamber.

The valve means may comprise a shuttle valve mounted for axial movementrelative to annular hot and cold seats to vary the relative proportionsof hot and cold water admitted to the mixing chamber. Preferably, thehot and cold seats are close together so that the water flows arebrought together and merge quickly. The shuttle valve may comprise acylindrical shuttle of short axial length mounted between the hot andcold seats and having an annular sealing face at each end forco-operating with the hot and cold seats. More preferably, however, thehot and cold seats are positioned between a pair of hot and coldshuttles having annular sealing faces for co-operating with the hot andcold seats. For example, the hot and cold seats may be provided byopposite sides of an annular seating member such as a washer. In thisway, the hot and cold flows may enter the mixing chamber atsubstantially the same axial position. In either arrangement, the hotseat at least may be resilient for enhanced sealing contact with theopposed sealing face of the shuttle to cut-off the flow of hot water.

Alternatively, the valve means may comprise a spool valve mounted foraxial movement relative to an annular flow separator to vary therelative proportions of hot and cold water admitted to the mixingchamber. The spool valve may comprise a cylindrical shuttle axiallymovable relative to an O-ring to vary the area of axially extendingslots in the shuttle to the flows of hot and cold water. Thisarrangement brings the flows of hot and cold water together quickly andpromotes mixing of the flows. The slots may be inclined to thelongitudinal axis of the shuttle so that the flows of hot and cold waterare offset in the circumferential direction. This causes the flows tointerlace and further promotes mixing of the flows.

Preferably, the flow of hot and cold water across the hot and cold seatsis in a radial inwards direction and both flows are then turned in anaxial direction to merge within the mixing chamber. For example, theflows may contact curved surfaces arranged to guide the flows in theaxial direction. One or both of the hot and cold flows may be providedwith a curved surface on the inboard edge of the porting such thatturning the flows in the axial direction is assisted by the Coandaeffect. Turning the flows in the axial direction creates an area of lowpressure on the upstream side of that flow that may be used to entrainand assist the other flow. This may usefully be employed where the hotwater flow is at a higher pressure to entrain the cold water flow andthereby improve the response of the thermal control system to change inthe desired temperature of the water.

The mixing chamber is preferably sized to match the total flow throughthe valve. The total flow is dependent on the combined waterwaycross-sectional areas at the hot and cold seats and is substantiallyconstant for all adjusted positions of the valve means. By sizing themixing chamber to match the permitted flow in this way, the velocityenergy of the hot and cold flows admitted to the mixing chamber islargely maintained. This contributes to the creation of turbulent flowwithin the mixing chamber that promotes thorough mixing of the hot andcold water flows. As a result, substantially complete mixing can beachieved over a relatively short distance from the point the hot andcold flows are brought together within the mixing chamber. In this way,fast, accurate response of the thermostat to changes in the desiredwater temperature is achieved by ensuring the thermostat is exposed towater that has been properly mixed and by reducing transport delays.

We have found that the above benefits and advantages are optimised ifthe cross-sectional area of the mixing chamber is from 1 to 1.5 timesand more preferably from 1 to 1.25 times the combined cross-sectionalareas of the hot and cold flows and the axial length of the mixingchamber is at least 5 times the width of the mixing chamber and morepreferably from 5 to 10 times the width of the mixing chamber.

The mixing chamber may be of any suitable shape and is preferably ofannular ring shape between inner and outer walls. In this way, the widthof the mixing chamber can be kept small thereby reducing the axiallength required to achieve complete mixing of the hot and cold flows. Asa result, the mixing chamber can be accommodated without having toincrease the overall size of the valve compared to existing valves.

Advantageously, the mixing chamber has smooth walls and is shaped toprovide substantially unobstructed flow with a gradual increase incross-sectional area in the direction of flow. In this way, mixing ofthe hot and cold flows is further enhanced and some of the velocityenergy required for turbulent flow may be recovered as pressure energyfor discharge of the mixed water from the valve.

Preferably, the temperature control means is linked to the valve meansfor user selection of a desired water temperature and is operable tomaintain the selected temperature substantially constant. In this way,user selection of a range of water temperatures, for example from coldto 60° C. may be permitted by any suitable means, for example arotatable control knob or push button or other means of temperatureselection.

The temperature control means may be of any suitable type commonlyemployed in thermostatic mixing valves to respond to a detecteddeviation of the mixed water temperature from the desired temperature toadjust the valve means to return the mixed water temperature to thedesired temperature. For example, the temperature control means maycomprise a thermostat containing a filler such as wax arranged to sensethe temperature of the mixed water and an actuator responsive toexpansion/contraction of the filler to adjust the valve means.Alternatively, the temperature control means may comprise at least onetemperature sensor such as a thermistor arranged to sense thetemperature of the mixed water and an actuator such as an electric motoroperable under the control of a controller such as a microprocessor toadjust the valve means.

The valve may include means for controlling the flow of hot and/or coldwater. The flow control may be separate from the temperature control ormay be linked to the temperature control.

In one arrangement, the flow control is separate from the temperaturecontrol and comprises flow control valves between the inlets and eachplenum chamber for controlling the flows of hot and cold water.Preferably the flow control valves are linked for operationsimultaneously by a common control member such as a rotatable flowcontrol knob or any other suitable means. For example, each flow controlvalve may comprise a sliding plate valve with at least one fixed valveplate and one movable valve plate for controlling flow. Preferably, themovable plate is adjustable between a closed position in which openingsin the plates are out of alignment to shut-off the flow and a range ofopen positions in which the openings overlap by varying amounts toadjust the flow. The plates may be ceramic plates.

In another arrangement, the flow control is linked to the temperaturecontrol and is operable to control the flows in sequence whereby thecold water flow is turned on first during start-up and the hot waterflow is turned off first during close-down. In this way, the watertemperature increases from full cold when the valve is initially turnedon and reduces to full cold again when the valve is finally turned off.

Preferably, the valve comprises a main body having the inlets forconnection to the hot and cold supplies and the outlet for connection toan ablutionary appliance and an opening for reception of a cartridgeunit housing the valve means. The outer chamber of each plenum chambermay be defined between the valve body and the cartridge unit with theinner chamber being formed inside in the cartridge unit andcommunicating with the outer chamber via at least one opening in thewall of the cartridge unit.

Preferably the cartridge unit carries seals, for example O-rings forsealing the cartridge unit in the valve body and separating the outerchambers. The O-rings may be of decreasing diameter from the outer endto the inner end of the cartridge unit to provide clearance forinsertion of the cartridge unit. In this way, fitment and removal of thecartridge unit is facilitated and sealing engagement is obtained whenthe cartridge unit is fully inserted in the valve body.

According to a second aspect of the invention we provide a thermostaticmixing valve for hot and cold water having two-stage inlet chambers forthe hot and cold water flows respectively, the inlet chambers beingarranged to distribute the flows uniformly with respect to porting foradmitting the flows to a mixing chamber to reduce asymmetric flowpatterns and promote thorough mixing of the flows within the mixingchamber.

According to a third aspect of the present invention we provide a methodof reducing asymmetric flow patterns and promoting thorough mixing offlows of hot and cold water within a mixing chamber of a thermostaticmixing valve comprising providing multi-stage inlet chambers for the hotand cold water flows respectively, and arranging the inlet chambers todistribute the flows uniformly with respect to porting for admitting theflows to a mixing chamber.

According to a fourth aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein the mixing chamber is sized to match the total flow through thevalve.

By sizing the mixing chamber to match the total flow through the valve,the velocity energy of the hot and cold flows admitted to the mixingchamber is largely maintained. This contributes to the creation ofturbulent flow within the mixing chamber that promotes thorough mixingof the hot and cold water flows. As a result, substantially completemixing can be achieved over a relatively short distance from the pointthe hot and cold flows are brought together within the mixing chamber.In this way, fast, accurate response to changes in the desired watertemperature is achieved by ensuring the control means responds to waterthat has been properly mixed and by reducing transport delays. As aresult, steady state operation to maintain a desired outlet watertemperature substantially constant is more reliable and transienttemperature overshoots/undershoots when the desired outlet watertemperature is adjusted by the user may be reduced.

This approach is totally different to the prior art. More especially,the present invention recognises and provides a solution to the problemsof incomplete mixing of the hot and cold flows on the accuracy andreliability of the thermal control systems employed to adjust therelative proportions of the hot and cold flows. In particular, thepresent invention enhances the mixing of the hot and cold flows bysizing the mixing chamber to create turbulent flow conditions. In thisway, the development of asymmetric flow patterns that tend to keep theflows separate is reduced or eliminated. As a result, substantiallycomplete mixing of the flows to provide a fully blended flow can beachieved within a mixing chamber of relatively small volume. Thisenables detection of the outlet water temperature to be carried out soonafter the flows have been brought together and enhances the response ofthe valve to changes in the desired water temperature.

The total flow through the valve is dependent on the combined waterwaycross-sectional areas of the hot and cold flows through the proportionalvalve means and is substantially constant for all adjusted positions ofthe valve means.

We have found that the above benefits and advantages are optimised ifthe cross-sectional area of the mixing chamber is from 1 to 1.5 timesand more preferably from 1 to 1.25 times the combined cross-sectionalareas of the hot and cold flows. In this way, turbulent flow conditionsare optimised and substantially complete mixing of the hot and coldflows can be achieved if the axial length of the mixing chamber is atleast 5 times the width of the mixing chamber and more preferably from 5to 10 times the width of the mixing chamber.

The mixing chamber may be of any suitable shape and is preferably ofannular ring shape between inner and outer walls. In this way, the widthof the mixing chamber can be kept small thereby reducing the axiallength required to achieve complete mixing of the hot and cold flows. Asa result, the mixing chamber can be accommodated without having toincrease the overall size of the valve compared to existing valves.

Advantageously, the mixing chamber has smooth walls and is shaped toprovide substantially unobstructed flow with a gradual increase incross-sectional area in the direction of flow. In this way, mixing ofthe hot and cold flows is further enhanced and some of the velocityenergy required for turbulent flow may be recovered as pressure energyfor discharge of the mixed water from the valve.

Each inlet preferably communicates with an annular outer chamber of atwo stage plenum chamber having an annular inner chamber separated fromthe outer chamber by partition means arranged so that water flows aroundthe outer chamber and into the inner chamber at a position axiallyspaced from the porting of the valve means.

In this way, the water is initially distributed around the outer chamberand approaches the porting in an axial direction within the innerchamber. As a result, swirling flow vectors are significantly reduced asthe water approaches the porting and the distribution of water volumeand velocity energy is substantially even around the porting for bothflows. This produces essentially identical mixing conditions for bothflows entering the mixing chamber that in turn leads to enhanced mixingthat avoids the formation of separate streams of mixed and unmixedwater.

Preferably, each plenum chamber is of similar size and shape so that thedistribution of flows is substantially the same. As a result, both flowsare matched so that any asymmetry is cancelled out when the flows mergewithin the mixing chamber. In this way, conditions in which separatestreams of mixed and unmixed water may be formed are eliminated to alarge extent.

The partition means separating the outer and inner chambers may be anannular wall provided with at least one opening for water to flow intothe inner chamber. Preferably, the opening provides a substantiallyuniform distribution of the water flow around the inner chamber. Forexample, the opening may be in the form of a continuous annular slot inthe wall between the outer and inner chambers. Alternatively, theopening may be in the form of a series of slots or holes of uniform sizeand shape formed in the wall between the outer and inner chambers with aregular spacing between the slots in the circumferential direction.

Preferably, the opening is offset relative to the point at which thewater flow enters the outer chamber. In this way, the water is preventedfrom flowing directly into the inner chamber and is confined to flowaround the outer chamber. This further contributes to a uniformdistribution of water flowing towards the porting within the innerchamber.

In a preferred arrangement, the opening is axially offset relative tothe point at which the water flow enters the outer chamber. In this way,the water flow is distributed around the outer chamber and approachesthe opening in an axial direction before flowing into the inner chamber.This leads to a further reduction in swirling flow vectors and enhancesuniform distribution of the water flow towards the porting within theinner chamber. By this use of two-stage plenum chambers, the incomingflows of hot and cold water are managed to produce conditions that helpto reduce asymmetric flow patterns and further promote thorough mixingof the water flows within the mixing chamber. More especially, theplenum chambers distribute the flows uniformly with respect to theporting for admitting the flows to the mixing chamber. In this way, thedevelopment of asymmetric flow patterns that tend to keep the flowsseparate is reduced or eliminated.

The valve means may comprise a shuttle valve mounted for axial movementrelative to annular hot and cold seats to vary the relative proportionsof hot and cold water admitted to the mixing chamber. Preferably, thehot and cold seats are close together so that the water flows arebrought together and merge quickly. The shuttle valve may comprise acylindrical shuttle of short axial length mounted between the hot andcold seats and having an annular sealing face at each end forco-operating with the hot and cold seats. More preferably, however, thehot and cold seats are positioned between a pair of hot and coldshuttles having annular sealing faces for co-operating with the hot andcold seats. For example, the hot and cold seats may be provided byopposite sides of an annular seating member such as a washer. In thisway, the hot and cold flows may enter the mixing chamber atsubstantially the same axial position. In either arrangement, the hotseat at least may be resilient for enhanced sealing contact with theopposed sealing face of the shuttle to cut-off the flow of hot water.

Alternatively, the valve means may comprise a spool valve mounted foraxial movement relative to an annular flow separator to vary therelative proportions of hot and cold water admitted to the mixingchamber. The spool valve may comprise a cylindrical shuttle axiallymovable relative to an O-ring to vary the area of axially extendingslots in the shuttle to the flows of hot and cold water. Thisarrangement brings the flows of hot and cold water together quickly andpromotes mixing of the flows. The slots may be inclined to thelongitudinal axis of the shuttle so that the flows of hot and cold waterare offset in the circumferential direction. This causes the flows tointerlace and further promotes mixing of the flows.

Preferably, the flow of hot and cold water across the hot and cold seatsis in a radial inwards direction and both flows are then turned in anaxial direction to merge within the mixing chamber. For example, theflows may contact curved surfaces arranged to guide the flows in theaxial direction. One or both of the hot and cold flows may be providedwith a curved surface on the inboard edge of the porting such thatturning the flows in the axial direction is assisted by the Coandaeffect. Turning the flows in the axial direction creates an area of lowpressure on the upstream side of that flow that may be used to entrainand assist the other flow. This may usefully be employed where the hotwater flow is at a higher pressure to entrain the cold water flow andthereby improve the response of the thermal control system to change inthe desired temperature of the water.

Preferably, the temperature control means is linked to the valve meansfor user selection of a desired water temperature and is operable tomaintain the selected temperature substantially constant. In this way,user selection of a range of water temperatures, for example from coldto 60° C. may be permitted by any suitable means, for example arotatable control knob or push button or other means of temperatureselection.

The temperature control means may be of any suitable type commonlyemployed in thermostatic mixing valves to respond to a detecteddeviation of the mixed water temperature from the desired temperature toadjust the valve means to return the mixed water temperature to thedesired temperature. For example, the temperature control means maycomprise a thermostat containing a filler such as wax arranged to sensethe temperature of the mixed water and an actuator responsive toexpansion/contraction of the filler to adjust the valve means.Alternatively, the temperature control means may comprise at least onetemperature sensor such as a thermistor arranged to sense thetemperature of the mixed water and an actuator such as an electric motoroperable under the control of a controller such as a microprocessor toadjust the valve means.

The valve may include means for controlling the flow of hot and/or coldwater. The flow control may be separate from the temperature control ormay be linked to the temperature control.

In one arrangement, the flow control is separate from the temperaturecontrol and comprises flow control valves between the inlets and eachplenum chamber for controlling the flows of hot and cold water.Preferably the flow control valves are linked for operationsimultaneously by a common control member such as a rotatable flowcontrol knob or any other suitable means. For example, each flow controlvalve may comprise a sliding plate valve with at least one fixed valveplate and one movable valve plate for controlling flow. Preferably, themovable plate is adjustable between a closed position in which openingsin the plates are out of alignment to shut-off the flow and a range ofopen positions in which the openings overlap by varying amounts toadjust the flow. The plates may be ceramic plates.

In another arrangement, the flow control is linked to the temperaturecontrol and is operable to control the flows in sequence whereby thecold water flow is turned on first during start-up and the hot waterflow is turned off first during close-down. In this way, the watertemperature increases from full cold when the valve is initially turnedon and reduces to full cold again when the valve is finally turned off.

Preferably, the valve comprises a main body having the inlets forconnection to the hot and cold supplies and the outlet for connection toan ablutionary appliance and an opening for reception of a cartridgeunit housing the valve means. The outer chamber of each plenum chambermay be defined between the valve body and the cartridge unit with theinner chamber being formed inside in the cartridge unit andcommunicating with the outer chamber via at least one opening in thewall of the cartridge unit.

Preferably the cartridge unit carries seals, for example O-rings forsealing the cartridge unit in the valve body and separating the outerchambers. The O-rings may be of decreasing diameter from the outer endto the inner end of the cartridge unit to provide clearance forinsertion of the cartridge unit. In this way, fitment and removal of thecartridge unit is facilitated and sealing engagement is obtained whenthe cartridge unit is fully inserted in the valve body.

According to a fifth aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein the mixing chamber has a cross-sectional area 1 to 1.5 times thecombined cross-sectional areas of the hot and cold flows through theproportioning valve means.

According to a sixth aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein the mixing chamber has an axial length at least 5 times thewidth of the mixing chamber.

According to a seventh aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein the mixing chamber has a cross-sectional area relative to thecombined cross-sectional areas of the hot and cold flows such that thevelocity energy of the hot and cold flows is sufficient to createturbulent flow conditions within the mixing chamber.

Preferably, the cross-sectional area of the mixing chamber is at leastequal to the combined cross-sectional areas of the hot and cold flows.

According to an eighth aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein the mixing chamber is arranged so that incoming streams of hotand cold water are turned to flow in the same direction such that flowof the hot stream entrains and assists flow of the cold stream.

By this invention, the incoming streams of hot and cold water aremanaged so that the interaction between the hot and cold streams tend toaid the temperature control process. In particular, flow of theentrained cold stream is increased by an increase in pressure of the hotstream tending to maintain the initial proportions of hot and cold waterand assist the response of the temperature control means to maintain thedesired temperature.

Preferably, the hot and cold streams enter the mixing chamber in aradial direction and are turned in an axial direction to merge withinthe mixing chamber. For example, one or both of the streams may contactcurved surfaces arranged to guide the streams in the axial direction.The curved surfaces may be provided by radially inner and outer walls ofthe mixing chamber. The inner wall may assist turning one of the streamsand the outer wall assist turning the other stream. In this way,undesirable crossing of the streams affecting the flow through the valvemay be reduced. Turning the water stream by the inner wall may beassisted by the Coanda effect.

Advantageously, the hot and cold streams enter the mixing chamber closetogether in the axial direction of flow whereby each stream entrains andassists the flow of the other stream. In this way an increase inpressure of either stream tends to increase the flow of the other streamto assist the response of the temperature control means to maintain thedesired temperature.

The valve means may comprise a shuttle valve mounted for axial movementrelative to annular hot and cold seats to vary the relative proportionsof hot and cold water admitted to the mixing chamber.

Preferably, the hot seat at least is resilient for enhanced sealingcontact with an opposed sealing face of the shuttle valve to cut-off theflow of hot water.

The shuttle valve may comprise a cylindrical shuttle of short axiallength mounted between the hot and cold seats and having annular sealingfaces at opposite ends for co-operating with the hot and cold seats.

More preferably, however, the hot and cold seats are positioned betweena pair of hot and cold shuttles having annular sealing faces forco-operating with the hot and cold seats. In this way, the hot and coldstreams enter the mixing chamber at substantially the same axialposition so that the streams are brought together and merge quickly topromote mixing of the streams.

In one arrangement, the hot and cold seats are provided by oppositesides of an annular seating member such as a washer. The seating membermay be incorporated in the valve body.

Alternatively, the valve means may comprise a spool valve mounted foraxial movement relative to an annular flow separator to vary therelative proportions of hot and cold water admitted to the mixingchamber.

The spool valve may comprise a cylindrical shuttle axially movablerelative to an O-ring to vary the area of axially extending slots in theshuttle to the streams of hot and cold water. This arrangement bringsthe streams of hot and cold water together quickly and promotes mixingof the streams.

The slots may be inclined to the longitudinal axis of the shuttle sothat the streams of hot and cold water are offset in the circumferentialdirection. This causes the streams to interlace and further promotesmixing of the streams.

Preferably, each inlet communicates with an annular outer chamber of atwo stage plenum chamber having an annular inner chamber separated fromthe outer chamber by partition means arranged so that water flows aroundthe outer chamber and into the inner chamber at a position axiallyspaced from the porting of the valve means.

In this way, the water is initially distributed around the outer chamberand approaches the porting in an axial direction within the innerchamber. As a result, swirling flow vectors are significantly reduced asthe water approaches the porting and the distribution of water volumeand velocity energy is substantially even around the porting for bothflows. This produces essentially identical mixing conditions for bothflows entering the mixing chamber that in turn leads to enhanced mixingthat avoids the formation of separate streams of mixed and unmixedwater.

Preferably, each plenum chamber is of similar size and shape so that thedistribution of flows is substantially the same. As a result, both flowsare matched so that any asymmetry is cancelled out when the flows mergewithin the mixing chamber. In this way, conditions in which separatestreams of mixed and unmixed water may be formed are eliminated to alarge extent.

The partition means separating the outer and inner chambers may be anannular wall provided with at least one opening for water to flow intothe inner chamber. Preferably, the opening provides a substantiallyuniform distribution of the water flow around the inner chamber. Forexample, the opening may be in the form of a continuous annular slot inthe wall between the outer and inner chambers. Alternatively, theopening may be in the form of a series of slots or holes of uniform sizeand shape formed in the wall between the outer and inner chambers with aregular spacing between the slots in the circumferential direction.

Preferably, the opening is offset relative to the point at which thewater flow enters the outer chamber. In this way, the water is preventedfrom flowing directly into the inner chamber and is confined to flowaround the outer chamber. This further contributes to a uniformdistribution of water flowing towards the porting within the innerchamber.

In a preferred arrangement, the opening is axially offset relative tothe point at which the water flow enters the outer chamber. In this way,the water flow is distributed around the outer chamber and approachesthe opening in an axial direction before flowing into the inner chamber.This leads to a further reduction in swirling flow vectors and enhancesuniform distribution of the water flow towards the porting within theinner chamber.

In this way, the development of asymmetric flow patterns that tend tokeep the flows separate is reduced or eliminated. As a result,substantially complete mixing of the flows to provide a fully blendedflow can be achieved within a mixing chamber of relatively small volume.This enables detection of the outlet water temperature to be carried outsoon after the flows have been brought together and enhances theresponse of the valve to changes in the desired water temperature.

The mixing chamber is preferably sized to match the total flow throughthe valve. The total flow is dependent on the combined waterwaycross-sectional areas at the hot and cold seats and is substantiallyconstant for all adjusted positions of the valve means. By sizing themixing chamber to match the permitted flow in this way, the velocityenergy of the hot and cold flows admitted to the mixing chamber islargely maintained. This contributes to the creation of turbulent flowwithin the mixing chamber that promotes thorough mixing of the hot andcold water flows.

As a result, substantially complete mixing can be achieved over arelatively short distance from the point the hot and cold flows arebrought together within the mixing chamber. In this way, fast, accurateresponse of the thermostat to changes in the desired water temperatureis achieved by ensuring the thermostat is exposed to water that has beenproperly mixed and by reducing transport delays.

We have found that the above benefits and advantages are optimised ifthe cross-sectional area of the mixing chamber is from 1 to 1.5 timesand more preferably from 1 to 1.25 times the combined cross-sectionalareas of the hot and cold flows and the axial length of the mixingchamber is at least 5 times the width of the mixing chamber and morepreferably from 5 to 10 times the width of the mixing chamber.

The mixing chamber may be of any suitable shape and is preferably ofannular ring shape between inner and outer walls. In this way, the widthof the mixing chamber can be kept small thereby reducing the axiallength required to achieve complete mixing of the hot and cold flows. Asa result, the mixing chamber can be accommodated without having toincrease the overall size of the valve compared to existing valves.

Advantageously, the mixing chamber has smooth walls and is shaped toprovide substantially unobstructed flow with a gradual increase incross-sectional area in the direction of flow. In this way, mixing ofthe hot and cold flows is further enhanced and some of the velocityenergy required for turbulent flow may be recovered as pressure energyfor discharge of the mixed water from the valve.

Preferably, the temperature control means is linked to the valve meansfor user selection of a desired water temperature and is operable tomaintain the selected temperature substantially constant. In this way,user selection of a range of water temperatures, for example from coldto 60° C. may be permitted by any suitable means, for example arotatable control knob or push button or other means of temperatureselection.

The temperature control means may be of any suitable type commonlyemployed in thermostatic mixing valves to respond to a detecteddeviation of the mixed water temperature from the desired temperature toadjust the valve means to return the mixed water temperature to thedesired temperature. For example, the temperature control means maycomprise a thermostat containing a filler such as wax arranged to sensethe temperature of the mixed water and an actuator responsive toexpansion/contraction of the filler to adjust the valve means.Alternatively, the temperature control means may comprise at least onetemperature sensor such as a thermistor arranged to sense thetemperature of the mixed water and an actuator such as an electric motoroperable under the control of a controller such as a microprocessor toadjust the valve means.

The valve may include means for controlling the flow of hot and/or coldwater. The flow control may be separate from the temperature control ormay be linked to the temperature control.

In one arrangement, the flow control is separate from the temperaturecontrol and comprises flow control valves between the inlets and eachplenum chamber for controlling the flows of hot and cold water.Preferably the flow control valves are linked for operationsimultaneously by a common control member such as a rotatable flowcontrol knob or any other suitable means. For example, each flow controlvalve may comprise a sliding plate valve with at least one fixed valveplate and one movable valve plate for controlling flow. Preferably, themovable plate is adjustable between a closed position in which openingsin the plates are out of alignment to shut-off the flow and a range ofopen positions in which the openings overlap by varying amounts toadjust the flow. The plates may be ceramic plates.

In another arrangement, the flow control is linked to the temperaturecontrol and is operable to control the flows in sequence whereby thecold water flow is turned on first during start-up and the hot waterflow is turned off first during close-down. In this way, the watertemperature increases from full cold when the valve is initially turnedon and reduces to full cold again when the valve is finally turned off.

Preferably, the valve comprises a main body having the inlets forconnection to the hot and cold supplies and the outlet for connection toan ablutionary appliance and an opening for reception of a cartridgeunit housing the valve means. The outer chamber of each plenum chambermay be defined between the valve body and the cartridge unit with theinner chamber being formed inside in the cartridge unit andcommunicating with the outer chamber via at least one opening in thewall of the cartridge unit.

Preferably the cartridge unit carries seals, for example O-rings forsealing the cartridge unit in the valve body and separating the outerchambers. The O-rings may be of decreasing diameter from the outer endto the inner end of the cartridge unit to provide clearance forinsertion of the cartridge unit. In this way, fitment and removal of thecartridge unit is facilitated and sealing engagement is obtained whenthe cartridge unit is fully inserted in the valve body.

According to a ninth aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein the proportioning valve means comprises a shuttle valve havingopposed sealing faces arranged for simultaneous movement relative torespective hot and cold valve seats positioned between the sealing facesfor controlling the relative proportions of hot and cold water admittedto the mixing chamber.

By positioning the hot and cold valve seats between opposed sealingfaces of the shuttle valve, the flows of hot and cold water are admittedto the mixing chamber close together in the axial direction and mixingof the flows is promoted. For example, the hot and cold valve seats maybe provided on opposite sides of a thin, plate member such as a washerextending between the sealing faces.

Preferably, the sealing faces are provided by hot and cold shuttlesshaped to assist turning the flows of hot and cold water in the sameaxial direction. For example, the shuttles may be provided with opposedcurved surfaces on radially inner and outer walls of the mixing chamber.The curved surface on the inner wall may assist turning the flow due tothe Coanda effect.

According to a tenth aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein the proportioning valve means comprises a shuttle valve having aproportioning shuttle axially slidable in a valve body relative to hotand cold seats for controlling the proportions of hot and cold wateradmitted to the mixing chamber, wherein the hot and cold seats areprovided by opposite sides of an annular seating member integral withthe valve body.

The seating member may comprise a thin, flat plate element such as awasher such that the flows of hot and cold water are admitted to themixing chamber close together in the axial direction.

The valve body and seating member may be united in a single component byarranging the seating member as an insert in a plastics moulding die forthe valve body.

According to an eleventh aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein the proportioning valve means comprises a shuttle valve having avalve body and a shuttle axially slidable in the valve body relative tohot and cold valve seats for controlling the relative proportions of hotand cold water admitted to the mixing chamber, the hot and cold seatsbeing provided between opposed sealing faces of the shuttle, and guidemeans for maintaining the sealing faces square with respect to the valveseats.

According to a twelfth aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein each of the flows of hot and cold water is admitted to themixing chamber at a plurality of openings.

Preferably, the hot flow openings alternate with the cold flow openingssuch that the flows interlace as they enter the mixing chamber therebypromoting mixing of the hot and cold water flows admitted to the mixingchamber.

Advantageously, the mixing chamber is of annular ring shape and theopenings are arranged so that the flows of hot and cold water are offsetin the circumferential direction causing the flows to interlace andpromote mixing of the flows within the mixing chamber.

In one arrangement, the openings are formed in a cylindrical shuttle ofa spool valve, the shuttle being mounted for axial movement relative toan annular flow separator to vary the relative proportions of hot andcold water admitted to the mixing chamber. For example, the shuttle maybe axially movable relative to an O-ring separator to vary the area ofaxially extending slots in the shuttle to the flows of hot and coldwater, the slots being inclined to the longitudinal axis of the shuttleso that the flows of hot and cold water are offset in thecircumferential direction causing the flows to interlace and promotemixing of the flows within the mixing chamber.

In another arrangement, the valve means controls the relativeproportions of hot and cold water admitted to separate hot and coldwater chambers and the openings are provided between the hot and coldwater chambers and the mixing chamber. For example, the hot and coldwater chambers may be arranged concentrically at one of the mixingchamber. The valve means may be a proportioning mechanism to adjust thehot and cold flows inversely to one another. Alternatively, the valvemeans may comprise two separate valves that are separately controlled.

According to a thirteenth aspect of the present invention we provide athermostatic mixing valve having a hot water inlet for connection to asupply of hot water, a cold water inlet for connection to a supply ofcold water, an outlet for temperature controlled water, valve means forcontrolling the relative proportions of hot and cold water admitted to amixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein the hot and cold water streams admitted to the mixing chamberare co-entrained.

Co-entraining the flows is beneficial in reducing potentiallyinstability effects caused by differences between the hot and cold waterpressures. Thus, if the water pressures are very different the streamsof hot and cold water will have very different levels of energy. If thestreams of hot and cold water entered the mixing chamber on oppositesides of the mixing chamber, there would be a risk that the higherenergy stream could suppress the flow of the lower energy stream,resulting in a sudden deviation from the intended proportions of hot andcold water. An instability of the whole valve could result.Co-entraining the flows reduces suppression of the flow of the lowerenergy stream by the higher energy stream.

Various other features, benefits and advantages of the inventedthermostatic mixing valve will be apparent from the descriptionhereinafter of exemplary embodiments.

This invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a front perspective view of a thermostatic mixing valveaccording to a first embodiment of the invention;

FIG. 2 is a front view, similar to FIG. 1, with the control knobs andcartridge cover removed;

FIG. 3 is an isometric sectioned view through the valve of FIG. 1;

FIG. 4 is a transverse section through the valve of FIG. 1;

FIG. 5 is a perspective view of a thermostatic mixing valve according toa second embodiment of the invention;

FIG. 6 is a longitudinal section through the valve of FIG. 5;

FIG. 7 is longitudinal section through the valve of FIG. 5 in partisometric projection;

FIG. 8 is an isometric sectioned view of part of the valve shown in FIG.6 as viewed from the left hand end of FIG. 6;

FIG. 9 is an isometric sectioned view of part of the valve shown in FIG.6 as viewed from the right hand end of FIG. 6;

FIG. 10 is a perspective view of a thermostatic mixing valve accordingto a third embodiment of the invention;

FIG. 11 is a perspective view of the body of the valve shown in FIG. 10with the cartridge unit removed;

FIG. 12 is a longitudinal section through the valve shown in FIG. 10;

FIG. 13 shows the section of FIG. 12 in part isometric projection;

FIG. 14 is a section of the hot seat insert of the valve shown in FIGS.10 to 13 in part isometric projection;

FIG. 15 is a perspective view of a thermostatic mixing valve accordingto a fourth embodiment of the invention;

FIG. 16 is a perspective view of the cartridge unit of the valve shownin FIG. 15;

FIG. 17 is a longitudinal section through the inlets of the valve shownin FIG. 15;

FIG. 18 is a longitudinal section through the outlet of the valve shownin FIG. 17;

FIG. 19 is an isometric view, partly sectioned, showing a modificationto the valve of FIGS. 15 to 18; and

FIG. 20 is a longitudinal section showing part of a thermostatic mixingvalve according to a fifth embodiment of the invention.

DETAILED DESCRIPTION

Referring first to FIGS. 1 to 4 of the accompanying drawings, athermostatic mixing valve 1 according to a first embodiment of theinvention is shown. The mixing valve 1 has inlets 2 and 3 for connectionto respective supplies of cold and hot water (not shown) and an outlet 4for discharging temperature controlled water to an ablutionary appliance(not shown) such as a spray fitting for a shower or other washingequipment. In this embodiment, each inlet 2,3 has two ports 2 a,2 b and3 a,3 b at right angles to each other for connecting the valve 1 tosupply pipes from above or behind the valve 1. A blanking plug (notshown) is provided for closing each port that is not connected to asupply pipe.

The valve 1 has a rotatable temperature control knob 5 detachablymounted on a drive spindle 6 of a temperature control mechanismdescribed in more detail later herein. The knob 5 is rotatable relativeto a fixed indicator ring 7 for user selection of a range ofoutlet-water temperatures, for example from cold to 60° C.

A stop (not shown) is provided to limit rotation of the knob 5 for userselection of outlet water temperatures up to a pre-set temperature, forexample 40° C. for safe washing/showering. The knob 5 includes anover-ride button 8 operable by the user to release the stop and allowselection of outlet water temperatures higher then the pre-settemperature up to the maximum.

In this way, accidental or inadvertent selection of an outlet watertemperature above the pre-set temperature is prevented but the user canpurposively select higher temperatures if desired. The stop isautomatically re-set when knob 5 is rotated to select a temperaturebelow the pre-set temperature.

The valve 1 also has an annular flow control ring 9 mounted on a drivespindle 10 of a flow control mechanism described in more detail laterherein. The control ring 9 is concentric with the control knob 5 and hasa lever 11 for manual rotation of the control ring 9 for user control ofa range of flows, for example from off to fully open.

As best shown in FIG. 2, the valve 1 has a body 12 with an oval opening13 in the front for reception of a cartridge unit 14 incorporating thetemperature control mechanism and flow control mechanism. The cartridgeunit 14 is releasably secured in the body 12 by four screws 15 and isprovided with cut-outs 16 in the marginal edge for releasably attachinga front cover 17 (FIG. 1) for the cartridge unit. The valve body 1 issymmetrical and the cartridge unit 14 can be fitted to allow connectionof the hot and cold supplies either way round to suit the installationlay-out.

With particular reference now to FIGS. 3 and 4, the flow controlmechanism includes a separate flow control valve 18,19 for each supply.Each valve 18,19 is similar and comprises an assembly of three ceramicdiscs 20,21,22. The outer discs 20,21 are fixed and the centre disc 22is movable relative thereto to vary the overlap of openings in the discsto control the flow through the valve. For the purposes of illustration,the valve 18 is shown fully open and the valve 19 is shown fully closed.It will be understood, however, that in use both valves 18,19 areassembled to open and close at the same time.

Each valve 18,19 is operatively connected to the control ring 9 by agear drive 23,24 for reciprocating movement of the associated centredisc 22 relative to the outer discs 20,21 in response to rotation of thecontrol ring 9 in opposite directions. The gear drives 23,24 are linkedto the control ring 9 for simultaneous adjustment to open and close bothvalves 18,19 in a synchronised manner. In this way, the selectedtemperature is substantially unaffected by adjustment of the valves18,19 to increase/decrease the total flow of water through the valve 1.

The temperature control mechanism includes a proportioning shuttle valve25 for controlling the relative proportions of hot and cold wateradmitted to an annular mixing chamber 26. The temperature controlmechanism also includes a wax thermostat 27 arranged to sense thetemperature of the mixed water and adjust the shuttle valve 25 tomaintain a selected temperature substantially constant.

The shuttle valve 25 comprises a pair of shuttle valve members 28,29mounted on the thermostat 27 and secured by a nut 30 screwed onto thethermostat 27. Each valve member 28,29 has an annular seal face 31,32arranged to co-operate with opposed annular seal faces 33,34 of anannular valve seat 35 positioned between the seal faces 31,32.

The valve members 28,29 are fixed relative to each other and are axiallymovable together relative to the valve seat 35 between a first endposition and a second end position. In the first end position, the valvemember 28 engages the valve seat 35 to shut-off the flow of cold water.In the second end position, the valve member 29 engages the valve seat35 to shut-off the flow of hot water. Between the end positions, thevalve members 28,29 are spaced from the valve seat 35 to control therelative proportions of hot and cold water admitted to the mixingchamber 26 according to the axial position of the valve members 28,29.

The valve seat 35 comprises a thin metal washer coated on both sideswith a layer of rubber or similar elastomeric material. In this way, theseal faces 33,34 are resilient for engagement with the seal faces 31,32of the shuttle valve members 28,29. As a result, fluid tight engagementof the valve members 28,29 with the valve seat 35 is assured in each ofthe end positions.

The thermostat 27 contains a wax filler and has an actuator rod 36 thatis axially movable in response to expansion/contraction of the waxfiller in response to temperature of the mixed water sensed by thethermostat 27. The free end of the rod 36 engages a cap 37 biasedtowards the rod 36 by an overload spring 38 acting between the cap 37and the inner end of a sleeve member 39 screwed into a threaded bore 40at the inner end of the drive spindle 6. The cap 37 and overload spring38 are retained in the sleeve member 39 by an end stop in the form of aU-shaped wire clip 37 a inserted through holes (not shown) in the sleevemember 39 to locate the cap 37 in a pre-loaded state.

The sleeve member 39 is axially slidable in the shuttle valve member 29and is located against rotation so as to be axially movable in responseto rotation of the drive spindle 6 by user actuation of the control knob5. In this way, axial movement of the sleeve member 39 in response touser selection of the desired water temperature is transmitted to theshuttle valve members 28,29 via the thermostat 25. As a result, theposition of the valve members 28,29 relative to the valve seat 35 isadjusted to vary the relative proportions of hot and cold water admittedto the mixing chamber 26 to produce mixed water having the selectedtemperature.

If the temperature of the mixed water increases, the wax filler expandsto increase the projecting length of the actuator rod 36. This causesthe thermostat 27 to be displaced axially away from the cap 37 againstthe biasing of a return spring 41 which is weaker than the overloadspring 38.

The thermostat 27 carries with it the shuttle valve members 28,29causing the seal face 32 to move towards the seal face 34 of the valveseat 35 to reduce the flow of hot water and simultaneously increase theflow of cold water by moving the seal face 31 away from the seal face 33of the valve seat 35. In this way the relative proportions of hot andcold water admitted to the mixing chamber 26 are adjusted to return thetemperature of the mixed water to the selected temperature.

If the temperature of the mixed water exceeds the maximum permitted, forexample if cold water supply fails, expansion of the wax filler causesthe valve member 29 to engage the valve seat 35 to shut-off the flow ofhot water. Further elongation of the actuator rod 36 is accommodated bycompression of the overload spring 38 to prevent damage to the internalcomponents of the cartridge unit 14.

If the temperature of the mixed water decreases, the wax fillercontracts and the thermostat 27 is displaced axially towards the cap 37reducing the projecting length of the rod 36 under the biasing of thereturn spring 41.

As a result of this movement, seal face 32 of shuttle member 29 movesaway from seal face 34 of the valve seat 35 to increase the flow of hotwater and simultaneously the flow of cold water is reduced by seal face31 of shuttle member 28 moving towards the seal face 33 of the valveseat 35. In this way the relative proportions of hot and cold wateradmitted to the mixing chamber 26 are adjusted to return the temperatureof the mixed water to the selected temperature.

As best shown in FIGS. 3 and 4, each flow control inlet valve 18,19leads to a two-stage plenum chamber 42,43 respectively. Each plenumchamber 42,43 is divided internally into concentric annular outer andinner chambers 42 a,43 a and 42 b,43 b by an axially extending partitionwall 44. In this embodiment, the partition wall 44 and valve seat 35 areintegrated in a single component by using the valve seat 35 as an insertin a plastic moulding die for the partition wall 44. In this way, thevalve seat 35 is an integral part of the cartridge body.

One end of the partition wall 44 forms a weir 45 separating the chambers42 a,42 b and the other end forms a weir 46 separating the chambers 43a,43 b. The weir 45 is axially spaced from the point of entry of coldwater to the outer chamber 42 a and the point of exit of cold water fromthe inner chamber 42 b. Likewise, the weir 46 is axially spaced from thepoint of entry of hot water to the outer chamber 43 a and the point ofexit of hot water from the inner chamber 43 b.

In this way, the incoming water to each plenum chamber 42,43 isdistributed around the outer chamber 42 a,43 a and is confined to flowin an axial direction towards the associated weir 45,46 where it flowsover the weir 45,46 into the inner chamber 42 b,43 b and is againconfined to flow in an axial direction towards the valve seat 35 whereit flows into the mixing chamber 26.

As a result, the water flows are uniformly distributed around theshuttle valve members 28,29 and swirling flow vectors are reduced tosubstantially insignificant values as the water approaches the valveseat 35. The velocity vectors as the water approaches the valve seat 35are substantially axial and the flow velocities across the valve seat 35are radially inwards and even all around the valve seat 35.

In this way, the distribution of water volume and velocity energy iseven around the valve seat 35 for both flows. As a result, the plenumchambers 42,43 provide substantially identical mixing conditions aroundthe porting of the shuttle valve members 28,29 that prevents asymmetricflow patterns developing to any significant extent as the hot and coldwater flows enter the mixing chamber 26.

Each shuttle valve member 28,29 is sealed relative to the cartridge bodyby an O-ring 47,48 respectively to close-off the inner chambers 42 b,43b. The diameter of the O-rings 47,48 is matched to that of the valveseat 35 so that the inlet water pressure exerts no resultant force onthe shuttle valve 25. The O-rings 47,48 also act to provide a guidancesystem for axial movement of the shuttle valve 25 that maintains thealignment of the shuttle valve 25 relative to the valve seat 35.

In this way, the seal faces 31,32 of the shuttle valve members 28,29 aremaintained square to the seal faces 33,34 of the valve seat 35. Thisfurther contributes to producing substantially identical mixingconditions around the porting of the shuttle valve members 28,29 thatprevents asymmetric flow patterns developing to any significant extentas the water flows enter the mixing chamber 26.

In addition to providing a uniform distribution of water volume andvelocity energy of the water flows, the arrangement of the valve seat 35between the seal faces 31,32 of the shuttle valve members 28,29 providesporting that enables the water flows to enter the mixing chamber 26close together. As a result, the flows meet radially inwardly of thevalve seat 35 and are swept into an axial direction by curved surfaces28 a,29 a of the shuttle valve members 28,29. In this way, interactionbetween the flows is enhanced to promote thorough mixing of the wateraround the valve seat 35 and the formation of separate streams of waterhaving different temperatures is substantially eliminated.

Moreover, velocity energy generated is maintained by matching thecross-sectional area of the mixing chamber 26 perpendicular to thedirection of flow to the combined cross-sectional area of the hot andcold flows across the valve seat 35. As a result, turbulent flowconditions are created within the mixing chamber 26 over the normal flowrates. Turbulent flow has numerous random eddies which give rise torandom lateral flows throughout the water stream that cause the hot andcold flows to merge producing a fully blended flow within a relativelyshort axial distance. More particularly, we have found that if thecross-sectional area of the mixing chamber 26 is 1 to 1½ times thecombined cross-sectional area of the hot and cold flows across the valveseat 35, substantially complete mixing of the hot and cold flows isachieved if the length of the mixing chamber 26 is approximately 5 timesthe width.

In this embodiment, the diameter of the shuttle valve 25 is largerelative to the operating stroke (or valve lift) and the mixing chamber26 has a relatively small width. This results in a compact size ofmixing chamber 26 that further promotes mixing of the water flows.

In addition, the mixing chamber 26 provides substantially unobstructedflow of water and can be slightly tapered to increase gradually thecross-sectional area in the direction of flow. As a result, some of thevelocity energy may be recovered and converted into pressure energy forthe mixed water discharged from the outlet 4.

Furthermore, in the circumstances where one of the flows has a higherpressure, the higher pressure flow creates a low pressure regionimmediately inside the mixing chamber causing the lower pressure flow toincrease and so assist the response of the thermostat 27 to maintain theselected temperature.

Thus, in the event the hot water pressure is higher, the flow of hotwater into the mixing chamber 25 is turned from a radial inwarddirection to an axial direction by curved surface 29 a. This creates alow pressure region causing the cold water flow to become entrained inthe hot water flow, mixing with it and tending to maintain the initialproportions of hot and cold water.

Alternatively, if the cold water pressure is higher, the flow of coldwater into the mixing chamber 25 clings to the curved surface 28 a dueto the Coanda effect and is turned into an axial direction. This createsa low pressure region causing the hot water flow to become entrained inthe cold water flow, mixing with it and tending to maintain the initialproportions of hot and cold water.

The mixed water leaving the mixing chamber 25 flows over the temperatureresponsive part 27 a of the thermostat 27. The thermostat 27 is exposedto water that is fully blended thereby improving the accuracy ofresponse to change in temperature of the blended water. Moreparticularly, we have found that temperature deviations from the desiredtemperature are reduced by approximately 50% to 70% compared to existingmixer valves in which the hot and cold water flows are not fullyblended. Also the speed of response to sudden temperature changes issimilarly improved.

An opening 49 in the inner end of the cartridge unit 14 allows the mixedwater to flow into an outlet chamber 50 defined between the cartridgeunit 14 and the valve body 12. The outlet chamber 50 communicates withthe outlet 4 for discharge of temperature controlled water to anablutionary appliance such as a shower handset (not shown) connected tothe outlet via a flexible hose (not shown).

Referring now to FIGS. 5 to 9 of the drawings, there is shown anelectronically controlled thermostatic mixing valve 101 according to asecond embodiment of the present invention. The mixing valve 101 hasspaced parallel inlets 102,103 for connection to supplies of hot andcold water (not shown) and two outlets 104,105 for dischargingtemperature controlled blended water. The outlets 104,105 are spacedapart 180 degrees for selective connection to an ablutionary appliancesuch as a shower spray fitting.

The mixing valve 101 may be provided in a range of sizes for differentapplications. For example, smaller valves may supply a single shower ora group of showers. Larger valves may be connected in a watercirculation system to provide a hot water circuit around a building inwhich the water is maintained at a constant temperature and can besupplied to a large number of appliances at different locations.

The valve 101 has a cylindrical body 106 with the outlets 104,105 at oneend and an opening 107 at the other end for reception of a cartridgeunit 108.

The cartridge unit 108 is a push fit in the body 106 and has an externalflange 109 that locates against the end of the body 106. The cartridgeunit 108 is releasably secured by an end plate 110 bolted to the body106 by a plurality of bolts 111 extending through aligned holes in theflange 109 to engage tapped holes (not shown) in the body 106.

The flange 109 carries a stepper motor 112 having a rotatable driveshaft 113 for actuating a spool valve 114 to vary the relativeproportions of hot and cold water admitted to an annular mixing chamber115 within the cartridge unit 108 as described later herein.

The cartridge unit 108 is sealed relative to the body 106 by threeaxially spaced O-rings 116,117,118 located in annular grooves119,120,121 respectively.

The O-ring 116 engages the inner surface of the body 106 adjacent theopening 107. The O-ring 117 is of smaller diameter and engages aninternal rib 122 axially spaced from the opening 107. The O-ring 118 isof smaller diameter still and engages an internal rib 123 axially spacedfrom the rib 122. The arrangement of the O-rings to be of progressivelysmaller diameter from the outer end of the cartridge unit 108 to theinner end facilitates insertion of the cartridge unit 108 in the body106. Thus, the O-ring 118 is a clearance fit in the body 106 until itengages rib 123 and O-ring 117 is a clearance fit until it engages rib122.

The cartridge unit 108 defines with the body 106 two annular outerchambers 124,125 separated by the O-ring 117. The inlet 102 opens to thechamber 124 and the inlet 103 opens to the chamber 125. Each chamber124,125 is of similar size and shape and the inlets 102,103 are arrangedin parallel on the same side of the body 106. In this way, water flowinginto the chambers 124,125 is distributed around the chambers 124,125 andany asymmetry in the distribution will be the same in each chamber124,125.

The spool valve 114 comprises a cylindrical spool sleeve 126 received ina cylindrical body 127 of the cartridge unit 108. The spool sleeve 126is sealed relative to the body 127 by three axially spaced O-rings128,129,130 located in annular grooves 131,132,133 formed in internalribs 134,135,135 a on the inside of the body 127.

The spool sleeve 126 defines with the body 127 two annular innerchambers 136,137 concentric with the outer chambers 124,125 andseparated by O-ring 129. Each chamber 136,137 is of similar size andshape.

The outer chamber 124 communicates with the inner chamber 136 via aseries of holes 138 formed in the body 127. The holes 138 arecircumferentially spaced apart and offset relative to the inlet 102 sothat water flowing into the outer chamber 124 is prevented from flowingdirectly into the inner chamber 136 and is confined to flow around theouter chamber 124.

The outer chamber 125 similarly communicates with the inner chamber 137via a series of holes 139 formed in the body 127. The holes 139 arecircumferentially spaced apart and offset relative to the inlet 103 sothat water flowing into the outer chamber 125 is prevented from flowingdirectly into the inner chamber 137 and is confined to flow around theouter chamber 125.

The spool sleeve 126 is provided with an internal hub 140 seated againstan internal rib 141 and secured by adhesive, welding or other suitablemeans. Attached to the hub 140 by a screw thread is a rearwardlyextending tubular portion 142 to locate axially a drive nut 143threadably engaging a lead screw portion 144 of drive shaft 113 betweena pair of stops 145,146.

The tubular portion 142 is located against rotation and guided for axialsliding movement by engagement of external axial splines 147 withinternal axial splines 148 of a tubular portion 149 secured to the endplate 110. In this way, the spool sleeve 126 is axially movable inresponse to rotation of the drive shaft 113 between end positionsdefined by engagement of the drive nut 143 with the stops 145,146.

The spool sleeve 126 is also provided with a tubular spout 150 seatedagainst an internal rib 151 and secured by adhesive, welding or thelike. The spout 150 extends away from the hub 140 and terminates in anoutlet chamber 152 communicating with the outlets 104,105.

The spool sleeve 126 is formed with a series of slots 153 uniformlyspaced apart in a circumferential direction and extending between theinternal ribs 141,151 at an angle relative to the longitudinal axis ofthe spool sleeve 126.

The O-ring 129 engages the spool sleeve 126 in the region of the slots153 whereby water can flow from each inner chamber 136,137 into themixing chamber 115 via the exposed portion of the slots 153. In thisway, axial movement of the spool sleeve 126 in response to rotation ofthe drive shaft 113 under the control of the motor 112 alters the areaof the slots 153 communicating with the chambers 136,137 to adjust therelative proportions of water admitted to the mixing chamber 115 fromeach chamber 136,137. The shape of the slots 153 may be adapted toprofile the rate of proportioning of hot and cold water according to theaxial position of the spool sleeve 126.

The outer end of the spout 150 is spaced from end wall 154 of the body106 opposite a pair of temperature sensors 155,156 mounted on a plug 157secured in an opening 158 in the end wall 154 by a plurality of bolts159 and sealed by an O-ring 159 a.

Water flowing from the mixing chamber 115 into the outlet chamber 152passes over the temperature sensors 155,156 and is swirled around in theoutlet chamber 152 by a pair of guide vanes 160,161 mounted on the plug157 to force the water to impart a rotation to the water stream enteringthe outlet chamber 152.

The temperature sensors 155,156 provide signals representative of thetemperature of the water leaving the mixing chamber 115 to amicroprocessor or other suitable control system (not shown) which inturn generates a control signal for actuating the stepper motor 112 toadjust the spool valve 114 to control the relative proportions of wateradmitted to the mixing chamber 115 in accordance with the desired outletwater temperature.

An axial control hole 162 through the body 127 of the cartridge unit 113connects each end of the spool valve 114 to the water pressure in theoutlet chamber 152 so that pressure forces acting on the spool sleeve126 are balanced and there is no net force tending to displace the spoolsleeve 126 in an axial direction.

In use, the inlets 102,103 are connected to supplies of hot and coldwater via on/off valves (not shown) that may also be adjustable to varythe flow similar to the ceramic plate valves of the first embodiment.Alternatively the on/off and flow control functions may be provided byseparate components.

The waterways are of similar size and shape whereby the connections tothe inlets 102,103 may be reversed without altering the operation andperformance of the valve 101.

The incoming water flows enter the outer chambers 124,125 where they areforced to flow around the chambers 124,125 by the offset arrangement ofthe inlets 102,103 relative to the holes 138,139 connecting the outerchambers 124,125 to the inner chambers 136,137.

The holes 138,139 open into the inner chambers 124,125 at the end spacedfrom the slots 153. As a result, the water entering the inner chambers136,137 is turned from a radial direction into an axial direction toflow towards the slots 153. In this way, the water flows are distributeduniformly and evenly around the spool sleeve 126 before arriving at theslots 153. If, however, any asymmetry remains in the flows, it will besimilar for each flow and produce matching ratios of hot and cold aroundthe spool sleeve 126 even if the total flow distribution is asymmetric.

The water arriving at the slots 153 flows into the mixing chamber 115 ina radial inwards direction and is swept into an axial direction betweencurved surfaces 140 a and 150 a of the hub 140 and spout 150respectively. As in the previous embodiment, both flows enter the mixingchamber 115 close together and the curved surfaces 140 a,150 a guide theflows to entrain one another. As shown, the centre of the mixing chamber115 is tapered away leading into the spout 150 and the total flow paththrough the mixing chamber 115 and spout 150 is designed to createturbulent flow over a distance sufficient to ensure substantiallycomplete mixing of the flows occurs before the water stream reaches thetemperature sensors 155,156.

More particularly, the mixing chamber 115 has a cross-sectional areaperpendicular to the direction of flow approximately 1 to 1½ times thecombined cross-sectional area of the hot and cold flows into the mixingchamber 115. As a result, velocity energy of the flows is maintainedcreating turbulent flow conditions within the mixing chamber 115 andsubstantially complete mixing of the hot and cold flows can be achievedif the length of the mixing chamber 115 is approximately 5 to 10 timesthe width.

By angling the slots 153 relative to the longitudinal axis of the spoolsleeve 126, the jets of hot and cold water entering the mixing chamber115 are offset around the circumference of the spool sleeve 126. As aresult, the two flows interlace as they enter the mixing chamber 115which further promotes mixing of the hot and cold water streams.

The spout 150 gradually expands towards the outer end so that the watervelocity reduces thereby recovering some of the velocity energy andconverting it to pressure energy. This can be beneficial in obtaininggood flow rates from small sized mechanisms and may not be required forlarger valves.

The temperature sensors 155,156 monitor the temperature of the waterstream exiting the spout 150 and send a signal representative of thetemperature to the control system e.g. a microprocessor, which in turnactuates the stepper motor 112 to adjust the axial position of the spoolsleeve 126 to vary the relative proportions of hot and cold wateradmitted to the mixing chamber 115 in accordance with the desired watertemperature. In this embodiment, the stepper motor 112 provides 1500steps between end positions of adjustment corresponding to full hot andfull cold. In this way, high temperature resolution is obtained forprecise control of the desired outlet water temperature.

The spout 150 is made of plastic or other suitable material having a lowthermal mass and conductivity. In this way, the temperature of the waterstream exiting the spout 150 is substantially unaffected by contact withthe spout 150 thereby improving the accuracy of the outlet watertemperature detected by the sensors 155,156.

The water flows entering the mixing chamber 115 are thoroughly mixedbefore reaching the temperature sensors 155,156. As a result, thesensors 155,156 can be small, e.g. thermistors, and sampled temperaturesare consistent with the average mixed water stream. In this way a largenumber of sensors and averaging of the detected temperatures is notrequired. In this embodiment, two sensors 155,156 are employed as aback-up to enable a sensor that has failed or is not working correctlyto be detected by comparing the signals from each sensor 155,156.

As will now be appreciated, each outer chamber 124,125 and associatedinner chamber 136,137 forms a two-stage plenum chamber for distributingthe water flows around the porting of the spool valve 114 to provide asubstantially uniform distribution of the flows entering the mixingchamber 115 similar to the first embodiment.

In addition, the hot and cold water flows enter the mixing chamber 115close together and are swept in an axial direction that promotesthorough mixing to produce a fully blended stream directed over thetemperature sensors 155,156. The temperature sensors 155,156 cantherefore be quick acting to provide rapid response of the controlsystem to change in the desired water temperature.

In a modification (not shown), the plug 157 is provided with a positionsensor to provide a signal to the control system representative of theposition of the spool sleeve 126. Position feedback may be employed ifthe incoming water supply pressures are unequal to compensate forincreased gain of the valve and provide accurate temperature controlnear to the limiting position of the spool sleeve 126 at which the gainis most noticeable.

Referring now to FIGS. 10 to 14 of the accompanying drawings, athermostatic mixing valve 201 according to a third embodiment of thepresent invention is shown. The valve 201 has inlets 202,203 forconnection to supplies of hot and cold water (not shown) and an outlet204 for discharging temperature controlled water to an ablutionaryappliance such as a shower (not shown).

The valve 201 has a drive spindle 205 for mounting a rotatabletemperature control knob (not shown) for user selection of a range ofoutlet water temperatures, for example from cold to 60° C.

As best shown in FIG. 11, the valve 201 has a body 206 with acylindrical bore 207 for reception of a detachable cartridge unit 208shown in FIGS. 12 and 13.

The body 206 has an external screw thread 209 at the open end of thebore 207 for engagement of a retainer ring 210 to secure the cartridgeunit 208 in the body 206.

The cartridge unit 208 is located in the correct orientation andprevented from rotating in the bore 207 by engagement of lugs (notshown) on the cartridge body 211 with a pair of diametrically opposednotches 212 in the body 206 of the valve at the open end of the bore207.

The cartridge unit 208 is sealed relative to the bore 207 of the valvebody 206 by three axially spaced O-rings 213,214,215 located in annulargrooves 216,217,218 in the outer surface of the cartridge body 211 toform two annular outer chambers 219,220 separated by the O-ring 214.

The inlets 202,203 lead to respective spiral ducts 202 a,203 a formed inthe wall of the valve body 206 that provide tangential entry of thewater flow to the outer chambers 219,220. Each outer chamber 219,220communicates with a respective annular inner chamber 221,222 via aseries of circumferentially spaced slots 223,224 formed in the cartridgebody 211.

The inner chambers 221,222 are separated by a shuttle valve 225 arrangedwithin the cartridge unit 208 for controlling the relative proportionsof hot and cold water admitted from the inner chambers 221,222 to anannular mixing chamber 226.

The shuttle valve 225 includes a shuttle 227 axially movable betweenannular valve seats 228,229. The cold water valve seat 228 is fixed andthe hot water valve seat 229 is provided by an insert 230 screwed intothe end of the cartridge body 211. In this way, the axial position ofthe hot seat 229 can be adjusted to vary the travel of the shuttle 227for different operating requirements.

As best shown in FIG. 14, the hot seat 229 is formed by an annularrubber ring 247 that is a stretch fit around an external rebate 248 atthe inner end of the insert 230 and has an annular groove 249 in theinner marginal surface for reception of a flange 250 to retain the ring247 in position. The ring 247 is stretched about 5% which holds it inplace under all operating conditions and is made of a fairly hard rubbercompound to provide a resilient seat for fluid tight engagement with theshuttle 227 to shut-off flow of the hot water under certain operatingconditions.

The shuttle 227 is connected by webs 231 to a mounting ring 232 locatedon a thermostat 233 and is biased by an overload spring 234 actingbetween the ring 232 and a retainer sleeve 235 screwed onto thethermostat 233. In this way, the shuttle 227 follows movement of thethermostat under normal operating conditions.

The thermostat 233 contains a wax filler and has an actuator rod 236that is axially movable in response to expansion/contraction of the waxfiller in response to the temperature of the mixed water sensed by thethermostat 233.

The free end of the rod 236 engages an axial plug 237 provided on theunderside of a drive nut 238. The plug 237 is slidably received in theend of the retainer sleeve 235 and provides an axial guide for one endof the thermostat assembly. The other end of the thermostat assembly isprovided with an axial guide in the form of internal webs 239 of a mixedwater guide 240 slidably received in the insert 230.

The guide 240 is biased by a return spring 241 towards the thermostat233 and engages the thermostat 233 via a spacer ring 245 having openings(not shown) for water to flow from the mixing chamber 226 through theguide 240 and into an outlet chamber 246 defined between the cartridgebody 211 and the valve body 206. The outlet chamber 246 communicateswith the outlet 204 for discharging temperature controller water.

The drive nut 238 is located against rotation in the cartridge body 211and is screwed into the inner end of the drive spindle 205 such that thedrive nut 238 is axially movable in response to user rotation of thecontrol spindle 205.

This axial movement is transmitted via the plug 237 to the thermostat233 for adjusting the position of the shuttle valve 227 between the hotand cold seats 228,229 to vary the relative proportions of hot and coldwater admitted to the mixing chamber 226 in accordance with userselection of the desired outlet water temperature.

If the temperature of the mixed water increases, the wax filler expandsto increase the projecting length of the actuator rod 236. This causesthe thermostat 233 to be displaced away from the plug 237 against thebiasing of the return spring 241 which is weaker than the overloadspring 234. The thermostat 233 carries with it the shuttle 227 causing ataper seal face 242 at one end to move towards the hot seat 229 toreduce the flow of hot water and a tapered seal face 243 at the otherend to move away from the cold seat 228 to increase the flow of coldwater. In this way, the relative proportions of hot and cold wateradmitted to the mixing chamber 226 are adjusted to return thetemperature of the mixed water to the selected temperature.

If the temperature of the mixed water exceeds the maximum permitted, forexample if the cold water supply fails, expansion of the wax fillercauses the shuttle valve 227 to image the hot seat 228 to shut-off theflow of hot water. Further elongation of the actuator rod 236 isaccommodated by compression of the overload spring 234 to prevent damageto the internal components of the cartridge unit 208.

If the temperature of the mixed water decreases, the wax fillercontracts and the thermostat 233 is displaced axially towards the plug237 reducing the projecting length of the rod 236 under the biasing ofthe return spring 241.

As a result, seal face 243 of the shuttle valve 227 moves towards thecold seat 228 to reduce the flow of cold water and seal face 242 movesaway from the hot seat 229 to increase the flow of hot water. In thisway, the relative proportions of hot and cold water admitted to themixing chamber 226 are adjusted to retain the temperature of the mixedwater to the selected temperature.

As best shown in FIGS. 12 and 13, incoming water is distributed aroundthe outer chambers 219,220 and flows into the inner chamber 221,222 viathe slots 223,224. The slots 223,224 are provided at the ends of theinner chambers 221,222 remote from the hot and cold seats 228,229. As aresult, the flow of hot and cold water is confined to flow in an axialdirection towards the hot and cold seats 228,229. In this way, the hotand cold water flows are evenly distributed around the inner chambers221,222 and pass across the hot and cold seats 228,229 in a radialdirection.

The cold water flow enters a chamber 244 surrounding the overload spring234 and is turned in an axial direction towards the mixing chamber 226.The hot water flow to the mixing chamber 226 is turned in an axialdirection by the curved inner surface 229 a of the hot seat 229. The hotwater clings to the surface 229 a due to the Coanda effect. As a result,both the hot and cold water flows are turned in the same directiontowards the mixing chamber 226 and are uniformly distributed around thethermostat 233 as they enter the mixing chamber 226.

The mixing chamber 226 has a small radial width compatible with therequired flow rates so that the two flows are thoroughly mixed in ashort axial distance. More particularly, the mixing chamber 226 has across-sectional area perpendicular to the direction of flowapproximately 1 to 1½ times the combined cross-sectional area of the hotand cold flows into the mixing chamber 226. As a result, velocity energyof the water flows is maintained creating turbulent flow conditionswithin the mixing chamber 226 and substantially complete mixing of thehot and cold flows can be achieved if the length of the mixing chamber226 is approximately 5 times the width.

The mixed water stream is then directed over the temperature responsivepart 233 a of the thermostat 233 by the guide 240. In this way, thethermostat 233 provides a fast, accurate response to change in thedesired mixed water temperature. Furthermore, if the hot water pressureis higher than the cold water pressure, a pressure drop is created bythe hot water entering the mixing chamber 226 that effectively entrainsand assists flow of cold water to assist response of the thermostat 233to maintain the desired water temperature.

As will be appreciated, each outer chamber 219,220 and associated innerchamber 221,222 forms a two stage plenum chamber for distributing waterflows around the shuttle 227. In this way, substantially identicalmixing conditions are created around the porting of the shuttle valve225 that prevent asymmetric flow patterns developing to any appreciableextent as the hot and cold water flows enter the mixing chamber 226.

In addition, the seal faces 242,243 of the shuttle 227 are maintainedsquare to the hot and cold seats 228,229 by the guide system for thethermostat 223. This further contributes to producing substantiallyidentical mixing conditions around the porting of the shuttle valve 225to reduce development of asymmetric flow patterns in the water admittedto the mixing chamber 226.

Referring now to FIGS. 15 to 18 of the accompanying drawings, there isshown a thermostatic mixing valve 301 according to a fourth embodimentof the present invention.

The mixing valve 301 has separate inlets 302,303 for connection tosupplies of hot and cold water (not shown) and an outlet 304 fordischarging temperature controlled water to an ablutionary appliancesuch as a shower (not shown).

The valve 301 has a hollow body 305 in which a detachable cartridge unit306 is received for controlling the flow and temperature of the waterdischarged from the outlet 304.

The cartridge unit 306 has a rotatable control spindle 307 with axialsplines 308 for detachably mounting a control knob (not shown) for acombined flow and temperature control mechanism described in more detaillater.

The cartridge unit 306 has an external screw thread 309 for engagementwith a mating internal screw thread of an opening at one end of the body305 to secure releasably the cartridge unit 306 in the body 306. Thecartridge unit 306 carries axially spaced O-rings 310,311 co-operablewith an internal wall 312 of the body 305 to define annular outerchambers 313,314.

The inlets 302,303 communicate with the outer chambers 313,314respectively. The outlet 304 communicates with an annular outlet chamber315 formed between the cartridge unit 306 of the valve body 305 and issealed by an O-ring 316.

Each outer chamber 313,314 communicates with an annular inner chamber317,318 within the cartridge unit 306 via a series of circumferentiallyspaced slots 319,320 formed in the body of the cartridge unit 306.

The slots 319,320 are axially offset relative to the inlets 302,303 sothat water entering the outer chambers 313,314 is distributed around thechambers 313,314 before entering the inner chambers 317,318.

The cartridge unit 306 has a shuttle valve 321 for controlling therelative proportions of hot and cold water admitted to an annular mixingchamber 322 in accordance with user selection of the desired outletwater temperature.

The shuttle valve 321 has a shuttle 323 axially movable between a coldwater valve seat 324 and a hot water valve seat 325 to control therelative proportions of hot or cold water admitted to the mixing chamber322.

The shuttle 323 has an O-ring 326 separating the inner chambers 317,318and is connected via webs 327 to a temperature overload housing 328mounted on a wax filled thermostat 329.

The thermostat 329 has an actuator rod 330 that is axially movable inresponse to expansion/contraction of the wax filler in response to thetemperature of the mixed water sensed by a temperature responsive part329 a of the thermostat 329.

The free end of the rod 330 engages a cap 331 received within thehousing 328 and biased towards the rod 330 by an overload spring 332acting between the cap 331 and an abutment collar 333 at the outer endof the housing 328. A return spring 334 acts between an insert 335screwed into the end of the cartridge body and the cap 331.

The insert 335 carries the hot seat 325 and is axially adjustable to setthe axial spacing between the hot seat 325 and cold seat 324 accordingto the operating requirements. The hot seat 325 is provided by a rubberring and is resilient as described for the previous embodiment toprovide a fluid-tight seal with the shuttle 323 to shut-off the flow ofhot water under certain operating conditions.

The insert 335 is provided with internal axial ribs 345 providing anaxial guide for the lower end of the overload housing 328. Thethermostat 329 provides an axial guide for the other end of the overloadhousing 328 and is in turn axially aligned by engagement with the piston336. In this way, the shuttle 323 is maintained square to the hot andcold seats 324,325 for axial adjustment of the position of the shuttle323 to vary the relative proportions of hot and cold water admitted tothe mixing chamber 322.

The other end of the thermostat 329 remote from the rod 330 is coupledto a piston 336 received in a bore 337 of a drive nut 338. The drive nut338 threadably engages the control spindle 307 and is located againstrotation so that rotation of the control spindle 307 causes axialmovement of the drive nut 338.

The lower end of the drive nut 338 is provided with an annular washer339 co-operable with an annular valve seat 340 provided by an annularflow guide 341 surrounding the temperature responsive part 329 a of thethermostat 329.

Rotation of the control spindle 307 in one direction lowers the drivenut 338 to cause the shuttle 323 to engage the hot seat 325 to shut-offthe flow of hot water. Further rotation of the control spindle 307 inthe same direction causes the thermostat 329 to move relative to thehousing 328 to compress the overload spring 332 and return spring 334until the washer 339 engages the valve seat 340 to cut-off the flow ofcold water.

Rotation of the control spindle 307 in the opposite direction moves thewasher 339 away from the valve seat 340 to allow flow of cold water withthe flow of hot water cut-off until the compression of the over-loadspring 332 is taken up. The housing 328 is then coupled for movementwith the thermostat 329 via the return spring 334 and further rotationof the control spindle in the same direction moves the shuttle 323 awayfrom the valve seat 325 to allow flow of hot water.

The amount of travel before the shuttle 323 is coupled for movement withthe thermostat 329 is pre-set by adjusting the position of the piston336 via an adjusting screw 342 threadably mounted in a tapped bore 343of the drive nut 338. The bore 343 extends axially to the outer end ofthe drive nut 338 for insertion of a tool such as a screwdriver or alienkey to adjust the position of the piston 336.

In use, hot and cold water flowing into the annular outer chambers313,314 is confined to flow around the chambers 313,314 and passesthrough the slots 319,320 into the inner chambers 317,318. The slots319,320 are axially offset relative to the valve seats 324,325 so thewater flows are evenly distributed around the chambers 317,318 andapproach the valve seats 324,325 in an axial direction.

The hot water flows across the valve seat 325 in a radial direction andis turned in an axial direction by a curved surface 328 a of the housing328. The hot water flow also clings to a curved surface 323 a of theshuttle 323 due to the Coanda effect that assists flow of the hot waterin the axial direction.

The cold water flows across the valve seat 324 in a radial direction andis turned in an axial direction by a curved surface 323 b of the shuttle323. The cold water flow also clings to a curved surface 324 a of theseat 324 due to the Coanda effect that assists flow of the cold water inthe axial direction.

The shuttle 323 is of short axial length so that both flows meet quicklyand are thoroughly mixed in the mixing chamber 322. More particularly,the mixing chamber 115 has a cross-sectional area perpendicular to thedirection of flow approximately 1 to 1½ times the combinedcross-sectional area of the hot and cold flows into the mixing chamber115. As a result, turbulent flow conditions are created within themixing chamber 322 and substantially complete mixing of the hot and coldflows can be achieved if the length of the mixing chamber 322 isapproximately 5 times the width. The mixed water stream flowing over thetemperature responsive part 329 a of the thermostat 329 within the flowguide 341 is substantially free from any streams of unmixed or partiallymixed water. As a result, the thermostat response is enhanced foraccurate adjustment of the shuttle 323 to control the relativeproportions of hot and cold water admitted to the mixing chamber 322according to the desired outlet water temperature.

The mixed water exiting from the flow guide 341 flows into the outletchamber 315 through a series of circumferentially spaced holes 344 inthe cartridge unit 306. The water flows from the outlet chamber 315 tothe outlet 304 for discharge to the ablutionary appliance.

If the desired temperature of the mixed water increases, the wax fillerexpands to increase the projecting length of the actuator rod 330. Thecauses the housing 328 to be displaced axially relative to thethermostat 329 against the biasing of the return spring 334. The housing328 carries with it the shuttle 323 causing the flow of hot water to bereduced and the flow of cold water to be increased. In this way therelative proportions of hot and cold water admitted to the mixingchamber 322 are adjusted to return the temperature of the mixed water tothe selected temperature.

If the temperature of the mixed water exceeds the maximum permitted, forexample if the cold water supply fails, expansion of the wax fillercauses the shuttle 323 to engage the hot seat 325 to shut-off the flowof hot water. Further elongation of the actuator rod 330 is accommodatedby compression of the overload spring 332 to prevent damage to theinternal components of the cartridge unit 306.

If the desired temperature of the mixed water decreases, the wax fillercontracts and the housing 328 is displaced axially towards thethermostat 329 reducing the projecting length of the rod 330 under thebiasing of the return spring 334. As a result, the axial position of theshuttle 323 is adjusted to increase the flow of hot water and reduce theflow of cold water entering the mixing chamber 322 to return thetemperature of the mixed water to the selected temperature.

As will be appreciated, each outer chamber 313,314 and associated innerchamber 317,318 forms a two stage plenum chamber for distributing waterflows around the shuttle 323. In this way, substantially identicalmixing conditions are created around the porting of the shuttle valve321 that prevent asymmetric flow patterns developing to any appreciableextent as the hot and cold water flows enter the mixing chamber 322.

In addition, the seal faces of the shuttle 323 are maintained square tothe hot and cold seats 324,325 by the guide system for the overloadhousing 328. This further contributes to producing substantiallyidentical mixing conditions around the porting of the shuttle valve 321to reduce development of asymmetric flow patterns in the water admittedto the mixing chamber 322.

Furthermore, the hot and cold flows are turned in an axial directiontowards the mixing chamber 322 which has a small radial width to createturbulent flow that ensures thorough mixing of the flows within a shortaxial distance. Moreover, the flows are introduced close together andturned in an axial direction so that, if either flow is at a higherpressure, it creates a pressure drop that entrains and assists the otherflow to enhance response of the thermostat to a change in the desiredtemperature of the outlet water.

Referring now to FIG. 19 of the accompanying drawings, there is shown amodification to the valve shown in FIGS. 14 to 18. For convenience, likereference numerals are used to indicate corresponding parts.

In the modification shown in FIG. 19, the inner chambers 317,318 areprovided with a series of axially extending flow guide vanes 346uniformly spaced apart in a circumferential direction. The guide vanes346 further assist in confining the water to flow in an axial directiontowards the porting of the shuttle valve 321 so that flow across thevalve seats 324,325 is radial. In this way swirl flow vectors in thewater admitted to the mixing chamber 322 are reduced. It will beunderstood that flow guide vanes 346 may be provided in the innerchambers of any of the previous embodiments.

Referring now to FIG. 20, there is shown part of an electronicallycontrolled thermostatic mixing valve 401 according to a fifth embodimentof the invention. This embodiment provides interlacing of the hot andcold streams to promote mixing in similar manner to the embodiment ofFIGS. 5 to 9 but with some advantages compared to the arrangement shownin FIGS. 5 to 9.

As shown the valve 401 has an inner water chamber 402 and a concentricouter water chamber 403. Valve means (not shown) controls the flow ofhot water to one of the chambers 402,403 and the flow of cold water tothe other chamber 402, 403. The valve means may be of any suitable typeto adjust the relative proportions of hot and cold water to control theoutlet water temperature in accordance with user selection and tomaintain the selected outlet water temperature substantially constant.

For example, the valve device may be a proportioning mechanism such as ashuttle valve or spool valve to adjust the hot and cold flows inverselyto each other. Alternatively, the valve device may comprise separateflow control valves for each flow. If separate valves are used, thetotal flow rate can be controlled by simultaneous adjustment of thevalves to increase or reduce both flows while keeping the relativeproportions the same to maintain the required outlet water temperature.

Each chamber 402, 403 is provided with a plurality of transfer ports ornozzles 402 a, 403 a respectively that open into a mixing chamber 404.The mixing chamber 404 has an annular ring shaped inlet portion 404 athat leads to a tubular exit portion 404 b that opens to an outletchamber (not shown) for discharge of temperature controlled output waterfrom the valve 401. The exit portion 404 b acts in the manner of adiffuser to recover some of the velocity energy in the water.

The chambers 402, 403 allow the flows of hot and cold water to bedistributed evenly before entering the mixing chamber 404 via thenozzles 402 a, 403 a. In this embodiment each chamber 402, 403 isprovided with twelve nozzles 402 a, 403 a uniformly spaced apart in acircumferential direction at one end of the mixing chamber 404 with thenozzles 402 a alternating with the nozzles 403 a. It will be understood,however that more or fewer nozzles 402 a, 403 a may be provided.

Arranging the nozzles 402 a, 403 a alternately causes the incoming flowsof hot and cold water to interlace and promote mixing within the mixingchamber 404 assisted by construction of the mixing chamber 404 to keepthe flows moving fast so that they are fully turbulent as describedpreviously.

The temperature of the mixed water stream is sensed by means of atemperature sensor 405 and the valve device is operable via anelectronic control system (not shown) such as a programmablemicroprocessor responsive to input of a desired output water temperatureand the temperature sensed by the sensor 405 to control the valvedevice, for example by means of an electric motor, to provide andmaintain the selected outlet water temperature.

The temperature sensor 405 has to be sited sufficiently downstream ofthe junction between the hot and cold streams in order to allow thestreams to merge enough for an accurate temperature to be measured. Thisgives rise to some transport delay due to the time it takes for thewater to travel from the junction to the sensor 405. The valve transientresponse to any change in the input parameters (pressures ortemperatures of the inlet water or the set temperature) is significantlyaffected by the transport delay. Therefore it is desirable that thestreams are mixed effectively and quickly.

We believe that the mixing may be substantially complete about 25% alongthe mixing chamber 404 from the junction of the hot and cold waterstreams with the rest of the mixing chamber 404 serving as a diffuser torecover some of the velocity energy in the water.

We have found interlacing of the streams of hot and cold water isparticularly effective in getting the streams to merge very quickly andenables the temperature sensor 405 to be positioned close to thejunction of the hot and cold streams. As a result, the transport delaymay be very short allowing any suitable valve device to be used tocontrol the hot and cold water streams.

In this embodiment, the entry nozzles 402 a, 403 a to the annular mixingchamber 404 can be sited close to one another Consequently the annularinlet portion 404 a of the mixing chamber 404 can be of small volume.Also the nozzles 402 a, 403 a are directed in substantially the samedirection so that the streams will entrain one another very effectively.

As a result, we have found that the temperature sensor 405 can bepositioned within the mixing chamber 404 closer to the junction betweenthe streams of hot and cold water compared to the embodiment of FIGS. 5to 9 where the incoming hot and cold streams are arranged on oppositesides of the O-ring separator.

In this embodiment, the nozzles 402 a, 403 a are arranged around anannular mixing chamber 404. This is a convenient way to provide thearrangement of interlaced nozzles 402 a, 403 a and keep the volume ofthe mixing annulus close to the size required to maintain turbulentflow. For example, in this embodiment we may provide nozzles 402 a, 403a approximately 3.28 mm in diameter arranged in a circle of meandiameter about 30 mm with the spout 404 b about 11.5 mm diameter at thesmallest point. It will be understood, however that other configurationscould be used that allow the interlacing of hot and cold water streamsand that keep the mixing chamber volume small.

In a modification (not shown) to the arrangement of FIG. 20, thechambers 402, 403 could be provided with annular slots that communicatewith the mixing chamber 404. Such arrangement also reduces transportdelays by bringing the hot and cold flows together quickly within themixing chamber and allows co-entrainment of the flows to reducesuppression of the flow of the lower energy stream by the higher energystream.

As will now be appreciated, in each of the above-described embodiments,the hot and cold water flows are effectively managed to produce a fullyblended stream of water flowing over the temperature responsive part ofthe thermal control system that results in improved thermal control ofthe outlet water temperature. More particularly, the effects oftemperature and/or pressure changes of one or both supplies on thedesired outlet water temperature are reduced to a level at which theyare substantially unnoticed by the user. Furthermore, the size andduration of transient temperature overshoots or undershoots produced bya change in the desired outlet water temperature are also reduced to alevel that is not uncomfortable and/or a risk to the user.

While the invention has been described with reference to the best meansknown to the applicant, it will be understood that the invention is notlimited to the exemplary embodiments above-described and is intended toinclude equivalents to any feature described herein. Moreover, theinvention is not intended to be limited to the combination of featuresdescribed in the exemplary embodiments and that the invention includesany novel feature described herein separately or in combination with anyother feature of any of the embodiments. Furthermore, it will beunderstood that other variations and modifications falling within thespirit and scope of the following claims are also included.

1. A thermostatic mixing valve having a hot water inlet for connectionto a supply of hot water, a cold water inlet for connection to a supplyof cold water, an outlet for temperature controlled water, valve meansfor controlling the relative proportions of hot and cold water admittedto a mixing chamber, the outlet communicating with the mixing chamber toreceive temperature controlled water having a desired temperature,temperature control means for adjusting the valve means in accordancewith the desired temperature of the temperature controlled water,wherein the valve means and the mixing chamber together form flowpassages for the incoming streams of hot and cold water and areconfigured such that the velocity of the incoming water streams ismaintained and the incoming water streams are turned to flow in the samedirection so that flow of one stream can entrain and assist flow of theother stream.
 2. A thermostatic mixing valve according to claim 1wherein the valve means is configured to increase the flow of the coldstream by an increase in pressure of the hot stream for maintaining theinitial proportions of hot and cold water admitted to the mixing chamberand assisting the response of the temperature control means to maintainthe desired temperature.
 3. A thermostatic mixing valve according toclaim 1 wherein the valve means is configured to cause the hot and coldstreams to enter the mixing chamber in a radial direction and turn in anaxial direction to merge within the mixing chamber.
 4. A thermostaticmixing valve according to claim 1 wherein the mixing chamber hasradially inner and outer walls including curved surfaces configured sothat the inner wall assists turning one of the streams and the outerwall assists turning the other stream.
 5. A thermostatic mixing valveaccording to claim 4 wherein the inner wall is configured so thatturning the water stream by the inner wall is assisted by the Coandaeffect.
 6. A thermostatic mixing valve according to claim 1 wherein thevalve means is configured so that the hot and cold streams enter themixing chamber close together in the axial direction of flow wherebyeach stream can entrain and assist flow of the other stream and anincrease in pressure of either stream increases the flow of the otherstream to assist the response of the temperature control means tomaintain the desired temperature.
 7. A thermostatic mixing valveaccording to claim 1 wherein the valve means is configured so that thehot and cold streams enter the mixing chamber at substantially the sameaxial position so that the streams are brought together and mergequickly to promote mixing of the streams.
 8. A thermostatic mixing valveaccording to claim 1 wherein the valve means is configured so that bothstreams are matched and any asymmetry is cancelled out when the streamsmerge within the mixing chamber.
 9. A thermostatic mixing valveaccording to claim 1 wherein the mixing chamber has a cross-sectionalarea perpendicular to the direction of flow that is matched to thecombined cross-sectional areas of the hot and cold flows through thevalve means.
 10. A thermostatic mixing valve according to claim 9wherein the cross-sectional area of the mixing chamber is from 1 to 1.5times the combined cross-sectional areas of the hot and cold flows. 11.A thermostatic mixing valve according to claim 9 wherein thecross-sectional area of the mixing chamber is from 1 to 1.25 times thecombined cross-sectional areas of the hot and cold flows.
 12. Athermostatic mixing valve according to claim 9 wherein the axial lengthof the mixing chamber is at least 5 times the width of the mixingchamber.
 13. A thermostatic mixing valve according to claim 9 whereinthe axial length of the mixing chamber is 5 to 10 times the width of themixing chamber.
 14. A thermostatic mixing valve according to claim 1wherein the mixing chamber has an annular ring shape between inner andouter walls and is configured to provide substantially unobstructed flowwith a gradual increase in cross-sectional area in the direction offlow.
 15. A thermostatic mixing valve according to claim 1 wherein thevalve means comprises a main body having the inlets for connection tothe hot and cold supplies and the outlet for connection to anablutionary appliance, the main body further having an opening forreception of a cartridge unit housing the valve means, wherein thecartridge unit carries seals for sealing the cartridge unit in the valvebody and the seals are O-rings of decreasing diameter from the outer endto the inner end of the cartridge unit to provide clearance forinsertion of the cartridge unit.